ContentLengthInputStream

/*
 * ====================================================================
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation.  For more
 * information on the Apache Software Foundation, please see
 * <http://www.apache.org/>.
 *
 */

package org.apache.http.impl.io;

import java.io.IOException;
import java.io.InputStream;

import org.apache.http.ConnectionClosedException;
import org.apache.http.io.BufferInfo;
import org.apache.http.io.SessionInputBuffer;
import org.apache.http.util.Args;

/**
 * Input stream that cuts off after a defined number of bytes. This class
 * is used to receive content of HTTP messages where the end of the content
 * entity is determined by the value of the {@code Content-Length header}.
 * Entities transferred using this stream can be maximum {@link Long#MAX_VALUE}
 * long.
 * <p>
 * Note that this class NEVER closes the underlying stream, even when close
 * gets called.  Instead, it will read until the "end" of its limit on
 * close, which allows for the seamless execution of subsequent HTTP 1.1
 * requests, while not requiring the client to remember to read the entire
 * contents of the response.
 *
 *
 * @since 4.0
 */
public class ContentLengthInputStream extends InputStream {

    private static final int BUFFER_SIZE = 2048;
    /**
     * The maximum number of bytes that can be read from the stream. Subsequent
     * read operations will return -1.
     */
    private final long contentLength;

    /** The current position */
    private long pos = 0;

    /** True if the stream is closed. */
    private boolean closed = false;

    /**
     * Wrapped input stream that all calls are delegated to.
     */
    private SessionInputBuffer in = null;

    /**
     * Wraps a session input buffer and cuts off output after a defined number
     * of bytes.
     *
     * @param in The session input buffer
     * @param contentLength The maximum number of bytes that can be read from
     * the stream. Subsequent read operations will return -1.
     */
    public ContentLengthInputStream(final SessionInputBuffer in, final long contentLength) {
        super();
        this.in = Args.notNull(in, "Session input buffer");
        this.contentLength = Args.notNegative(contentLength, "Content length");
    }

    /**
     * <p>Reads until the end of the known length of content.</p>
     *
     * <p>Does not close the underlying socket input, but instead leaves it
     * primed to parse the next response.</p>
     * @throws IOException If an IO problem occurs.
     */
    @Override
    public void close() throws IOException {
        if (!closed) {
            try {
                if (pos < contentLength) {
                    final byte buffer[] = new byte[BUFFER_SIZE];
                    while (read(buffer) >= 0) {
                        // do nothing.
                    }
                }
            } finally {
                // close after above so that we don't throw an exception trying
                // to read after closed!
                closed = true;
            }
        }
    }

    @Override
    public int available() throws IOException {
        if (this.in instanceof BufferInfo) {
            final int len = ((BufferInfo) this.in).length();
            return Math.min(len, (int) (this.contentLength - this.pos));
        }
        return 0;
    }

    /**
     * Read the next byte from the stream
     * @return The next byte or -1 if the end of stream has been reached.
     * @throws IOException If an IO problem occurs
     * @see java.io.InputStream#read()
     */
    @Override
    public int read() throws IOException {
        if (closed) {
            throw new IOException("Attempted read from closed stream.");
        }

        if (pos >= contentLength) {
            return -1;
        }
        final int b = this.in.read();
        if (b == -1) {
            if (pos < contentLength) {
                throw new ConnectionClosedException(
                                "Premature end of Content-Length delimited message body (expected: %,d; received: %,d)",
                                contentLength, pos);
            }
        } else {
            pos++;
        }
        return b;
    }

    /**
     * Does standard {@link InputStream#read(byte[], int, int)} behavior, but
     * also notifies the watcher when the contents have been consumed.
     *
     * @param b     The byte array to fill.
     * @param off   Start filling at this position.
     * @param len   The number of bytes to attempt to read.
     * @return The number of bytes read, or -1 if the end of content has been
     *  reached.
     *
     * @throws java.io.IOException Should an error occur on the wrapped stream.
     */
    @Override
    public int read(final byte[] b, final int off, final int len) throws java.io.IOException {
        if (closed) {
            throw new IOException("Attempted read from closed stream.");
        }

        if (pos >= contentLength) {
            return -1;
        }

        int chunk = len;
        if (pos + len > contentLength) {
            chunk = (int) (contentLength - pos);
        }
        final int readLen = this.in.read(b, off, chunk);
        if (readLen == -1 && pos < contentLength) {
            throw new ConnectionClosedException(
                            "Premature end of Content-Length delimited message body (expected: %,d; received: %,d)",
                            contentLength, pos);
        }
        if (readLen > 0) {
            pos += readLen;
        }
        return readLen;
    }


    /**
     * Read more bytes from the stream.
     * @param b The byte array to put the new data in.
     * @return The number of bytes read into the buffer.
     * @throws IOException If an IO problem occurs
     * @see java.io.InputStream#read(byte[])
     */
    @Override
    public int read(final byte[] b) throws IOException {
        return read(b, 0, b.length);
    }

    /**
     * Skips and discards a number of bytes from the input stream.
     * @param n The number of bytes to skip.
     * @return The actual number of bytes skipped. &le; 0 if no bytes
     * are skipped.
     * @throws IOException If an error occurs while skipping bytes.
     * @see InputStream#skip(long)
     */
    @Override
    public long skip(final long n) throws IOException {
        if (n <= 0) {
            return 0;
        }
        final byte[] buffer = new byte[BUFFER_SIZE];
        // make sure we don't skip more bytes than are
        // still available
        long remaining = Math.min(n, this.contentLength - this.pos);
        // skip and keep track of the bytes actually skipped
        long count = 0;
        while (remaining > 0) {
            final int readLen = read(buffer, 0, (int)Math.min(BUFFER_SIZE, remaining));
            if (readLen == -1) {
                break;
            }
            count += readLen;
            remaining -= readLen;
        }
        return count;
    }
}